To generate Cherenkov radiation (CR) in natural medium, the electron energy threshold is higher than hundreds of keV. Even though various approaches were adopted, the high-energy electrons as high as tens of keV is still required in experiment. Here we proposed to eliminate the threshold of electron energy to generate CR with the help of hyperbolic metamaterial (HMM). The analytical and simulation results indicate that, even though electron energy is lower than 0.1keV, the CR could be obtained in HMM in a visible and near-infrared frequency region. Further, the on-chip integrated threshold-less CR source, consisted with a planar electron emitter, Au-SiO<sub>2</sub> multilayers HMM, and periodic metal nano-slits, has been realized. It is demonstrated that, with low-energy electrons (0.25-1.4keV), the CR is generated covering &lambda;0=500~900nm. The electron energy generating CR experimentally is two~three orders of magnitude lower than that in natural media and artificial structures. As we know, this is the first on-chip integrated free electron light source benefiting from the threshold-less CR. Although less than 1% of the light energy could be coupled to free space, the total output light power still reaches 200nW, which is two orders of magnitude higher than free electron light source by using other nanostructures.

We propose and experimentally demonstrate a generation scheme of telecom-band fiber-based frequency-degenerate polarization-entanglement photon pair source. Basing on the vector spontaneous four wave mixing process in a Sagnac fiber loop along the clockwise and counter-clockwise directions, two frequency-degenerate and polarization orthogonal biphoton states generate and then lead to the polarization entanglement states by the interference at the beamsplitter. The raw fringe visibilities of the two-photon interferences are 97% and 92%, respectively. Information can be encoded on the generated photon pairs using the polarization entangled Bell states. It is demonstrated by a simplified Bell state measurement with a fringe visibility of 83%.

Optical biosensors with the high sensitivity is an important tool for environment monitoring, disease diagnosis and drug development. Integrating the biosensor could reduce the size and cost and is desirable for home and outdoor use. However, the integrated structure always results in the worsening of sensitivity and narrowing of sensing range, especially for small molecule sensing. In this work, we propose an integrated plasmonic biosensor based on the resonant structure composed of dielectric grating and metal film. With vertically incident light from the grating side, the surface plasmon polariton (SPP) mode could be excited at certain wavelength and the reflected light would vanish. Simulation results indicate that, when varying refractive index (n<sub>det</sub>) of detection layer, the energy of reflected light changes dramatically. Assuming the resolution of the power meter is 0.01dB, the sensing resolution could be 4.37×10<sup>-6</sup> RIU, which is very close to the bulk lens based SPP biosensor by monitoring the light intensity variation. Since antibody and antigen always have the size of tens of nanometers, it is necessary to check the sensing ability of the sensor in tens of nanometers. Fixing n<sub>det</sub> and varying the thickness of detection layer, calculation result demonstrates that the reflected light energy is sensitive to the thickness change with one hundred nanometers. This attributes to the surface mode property of SPP mode.

Optomechanical crystal is a combination of both photonic and phononic crystal. It simultaneously confines light and mechanical motion and results in strong photon-phonon interaction, which provides a new approach to deplete phonons and realize on-chip quantum ground state. It is promising for both fundamental science and technological applications, such as mesoscopic quantum mechanics, sensing, transducing, and so on. Here high optomechanical coupling rate and efficiency are crucial, which dependents on the optical-mechanical mode-overlap and the mechanical frequency (phonon frequency), respectively. However, in the conventional optomechanical-crystal based on the same periodical structure, it is very difficult to obtain large optical-mechanical mode-overlap and high phonon frequency simultaneously. We proposed and demonstrated nanobeam cavities based on hetero optomechanical crystals with two types of periodic structure. The optical and mechanical modes can be separately confined by two types of periodic structures. Due to the design flexibility in the hetero structure, the optical field and the strain field can be designed to be concentrated inside the optomechanical cavities and resemble each other with an enhanced overlap, as well as high phonon frequency. A high optomechanical coupling rate of 1.3 MHz and a high phonon frequency of 5.9 GHz are predicted theoretically. The proposed cavities are fabricated as cantilevers on silicon-on-insulator chips. The measurement results indicate that a mechanical frequency as high as 5.66 GHz is obtained in ambient environment, which is the highest frequency demonstrated in one-dimensional optomechanical crystal structure.

Nanostructure is an effective solution for realizing optoelectronic devices with compact size and high performances simultaneously. This paper reports our research progress on integrated nanophotonic devices for optical interconnections. We proposed a parent-sub micro ring structure for optical add-drop multiplexer (OADM) with compact footprint, large free spectral range, and uniform channel spacing. All eight channels can be multiplexed and de-multiplexed with 2.6 dB drop loss, 0.36 nm bandwidth (&gt;40 GHz), -20 dB channel crosstalk, and high thermal tuning efficiency of 0.15 nm/mW. A novel principle of optical switch was proposed and demonstrated based on the coupling of the defect modes in photonic crystal waveguide. Switching functionality with bandwidth up to 24 nm and extinction ratio in excess of 15 dB over the entire bandwidth was achieved, while the footprint was only 8 &mu;m×17.6 &mu;m. We proposed an optical orbital angular momentum (OAM) coding and decoding method to increase the data-carrying capacity of wireless optical interconnect. An integrated OAM emitter, where the topological charge can be continuously varied from -4 to 4 was realized. Also we studied ultrafast modulated nLED as the integrated light source for optical interconnections using a nanobeam cavity with stagger holes.

In this paper, we proposed and demonstrated a simple ChG waveguide structure, guided by low refractive-index
strips on the surfaces of planar ChG films. Theoretical analysis shows that it supports quasi-TE mode transmission in
1.5μm band with high nonlinearity. Samples of this surface guiding ChG waveguides are fabricated. Its transmission
properties are measured by the cut-off method, showing a waveguide attenuation of 0.67dB/mm and a coupling loss with
optical fibers of ~8dB/facet. It provides a simple way to realize high quality ChG waveguides, which has great potential
in developing nonlinear photonic devices.

Here we present investigations on utilizing two kinds of plasmonic nanoparticles (NPs) to enhance
the efficiency of dye sensitized solar cells (DSCs). The Au@PVP NPs is proposed and present the
specialty of adhesiveness to dye molecules, which could help to localize additional dye molecules near
the plasmonic NPs, hence increasing the optical absorption consequently the power conversion
efficiency (PCE) of the DSCs by 30% from 3.3% to 4.3%. Meanwhile, an irregular Au-Ag alloy
popcorn-shaped NPs (popcorn NPs) with plenty of fine structures is also proposed and realized to
enhance the light absorption of DSC. A pronounced absorption enhancement in a broadband
wavelength range is observed due to the excitation of localized surface plasmon at different
wavelengths. The PCE is enhanced by 32% from 5.94% to 7.85%.

Broadband thermo-optic switch based on an ultra-compact W2 photonic crystal waveguide (PCW) is demonstrated with
an integrated titanium/aluminum microheater on its surface. The operating principle relies on shifting a transmission-dip
caused by the enhanced coupling between the defect modes in W2 PCW. As a result, broadband switching functionality
with larger extinction ratio can be attained. Moreover, microheaters with different width are evaluated by the power
consumptions and heating transfer efficiency, and an optimized slab microheater is utilized. Finally, switching
functionality with bandwidth up to 24 nm (1557~1581 nm) is measured by the PCW with footprint of only
8&mu;m×17.6 &mu;m, while the extinction ratio is in excess of 15 dB over the entire bandwidth. What’s more, the switching speed is obtained by the measurement of alternating current modulation. Response time for this thermo-optic switch is
11.0&plusmn;3.0 &mu;s for rise time and 40.3&plusmn;5.3 &mu;s for fall time, respectively.

Single photon sources (SPSs) play important roles in quantum communication and quantum information processing.
Spontaneous four wave mixing (SFWM) in optical fibers provides a promising way to realize practical heralded single
photon sources (HSPSs), since it is compatible with current techniques of optical communications. In this paper, two
independent HSPSs at 1.5&mu;m band are realized in one polarization maintaining dispersion shifted fiber (PM-DSF)
utilizing its large birefringence. When pulsed pump light passes through an optical fiber, two kinds of SFWM will take
place simultaneously. One is scalar processes, in which two annihilated pump photons and generated photon pair are all
polarized along the same fiber polarization axis. The other is vector processes, in which two annihilated pump photons
are polarized along different fiber polarization axes, either for the two photons of the generated pair. In the PM-DSF, the
large birefringence generates obvious walk-off effect on the two pump polarization components, which leads to an
effective suppression of the vector processes. Hence, by proper pump polarization, correlated photon pairs (CPPs) with
different polarization directions can be generated independently by the two scalar processes, which can be used to realize
two independent HSPSs. The indistinguishability of the heralded photons generated by the two independent sources is
demonstrated by an experiment of Hong-Ou-Mandel (HOM) interference. Using a fiber coupler as the beam splitter, a
visibility of HOM dip of 76% is achieved, showing their potential on quantum information.

This paper introduces our recent works on quantum light sources based on third-order nonlinear waveguides. Based on
the spontaneous four wave mixing (SFWM) effect in optical fibers, we realized high quality correlated photon pair
generation. A fiber based heralded single photon source (HSPS) with a preparation efficiency of ~80% under a g<sup>2</sup>(0) of
0.06 was realized based on it. On the other hand, we demonstrated that the vector scattering processes of the SFWM can
be suppressed effectively by the polarization walk off effect in the polarization maintaining fibers (PMFs), by which
polarization entangled photon pair generation was realized in a piece of PMF experimentally. We also realized correlated
photon pair generation in silicon wire waveguides fabricated by ourselves, demonstrating its low noise performance.
These works shows that SFWM in third-order nonlinear waveguides provides a promising way to realize practical
quantum light sources compatible with today’s engineering technologies.

Single photons are essential resource for quantum communication and quantum information processing, which can carry
quantum information to distant locations. A promising scheme for single photon generation is the heralded single photon
source (HSPS), which is based on the generation of correlated photon pairs (CPPs). Utilizing the quantum correlation
property of the CPPs, one photon of the CPP is detected providing an electrical signal to herald the other photon as a
single photon output. Recently, 1.5 &mu;m CPP generation through spontaneously four wave-mixing (SFWM) in fiber has
focused much attention, which provides a practical way to realize 1.5 &mu;m fiber-based HSPS. The quality of a HSPS is
described by the preparation efficiency and g<sup>(2)</sup>(0). In the fiber-based HSPS, the preparation efficiency is determined by
the loss of the filtering and splitting system and the noise photons generated by spontaneously Raman scattering (SpRS).
Considering the impact of the SpRS can be reduced by cooling the fiber and optimizing the frequency detuning of
filtering and splitting system, the loss of the filtering and splitting system may give a theoretical up-limit of the
preparation efficiency. In this paper, using commercial fiber components, we realize a high quality HSPS based on
cooled fiber with a preparation efficiency of 80% under a g<sup>(2)</sup>(0) of0.06, showing its great potential in the application of
quantum information technology.

In particular, the surface plasmon polariton (SPP) is attractive to enhance the spontaneous emission (SE) from active
materials due to the larger density of state (DOS) and smaller mode volume comparing with optical wave, namely
Purcell effect. Usually, the Purcell factor (PF) is calculated from the reduced form of Fermi’s golden rule, where only the
DOS and mode volume of photon (or SPP mode) are involved. Obviously, the PFs calculated with reduced form exclude
the influence of active material and only evaluate the effect of cavity or SPP waveguide. However, for a practical
emitter, the linewidth could not always be ignored. For example, the ensemble emission linewidth of mass Si- quantum
dots (QD) is about 220meV~400meV (90~160nm), which are much wider than the linewidth of the SPP DOS
In this work, the PF of SPP mode on Au-Si<sub>3</sub>N<sub>4</sub> grating is calculated with full integration formula of Fermi’s golden rule by taking account of the spontaneous emission linewidth from single Si-QD. The calculated PF is about 1.7~1.4 within the emission range of <i>&dagger;h&omega;<sub>0</sub></i> =1.9~1.6eV. Comparing with the PF value of 266.9~30.1, which is calculated without including the emission linewidth of Si-QD, it could be easily concluded that the impact of rather wide emission linewidth is fatal for applying plasmonic enhancement. To obtain some useful guidelines, we also discuss the necessary linewidth for effective plasmonic enhancement on Si-QDs. It is found that if the emission linewidth could be decreased to several tens of &mu;eV, plasmonic enhancement would be helpful.

Optical enhancement of organic solar cells with rectangular metallic gratings as the back
contact has been investigated numerically. It is demonstrated that a strongly increased light absorption
up to 37% with the plasmonic enhanced effect of metallic gratings has been obtained. In addition, we
study the light absorption enhancement at oblique incidence and also get a high absorption
enhancement within the incident angle of 30 degree.

The plasmonic enhanced absorption for thin film solar cells with silver nanoparticles (NPs) deposited on top of the
amorphous silicon film (a-Si:H) solar cells and embedded inside the active layer of organic solar cells (OSCs) has been
simulated and analyzed. Obvious optical absorption enhancement is obtained not only at vertical incidence but also at
oblique incidence. By properly adjusting the period and size of NPs, an increased absorption enhancement of about
120% and 140% is obtained for a-Si:H solar cells and OSCs, respectively.

Coupling between long range surface plasmon polariton (LRSPP) waveguide mode and dielectric waveguide (DW)
mode has been studied theoretically and experimentally. It is demonstrated that the fundamental and second-order
TM-polarized mode of dielectric waveguide could couple with LRSPP mode efficiently, respectively.

A vertical coupler composed of short range surface plasmon polariton waveguide and dielectric waveguide is studied
theoretically and experimentally. The short range surface plasmon polariton mode is excited efficiently by the dielectric
waveguide mode within tens of microns. Meanwhile, based on the hybrid coupler, a highly compact polarizer and a high
performance sensor for ultra-thin layer sensing could be achieved.

We demonstrated and fabricated a 20&mu;m-long ultra-compact variable optical attenuator based on thermo-optical effect
with slow light photonic crystal waveguide (PCWG). In simulation, we optimize the line-defect width and radius/period
ratio (<i>r/a</i>) of the PCWG for deep photonic band gap and large slope photonic band edge. An <i>r/a</i>=140nm/410nm W1
PCWG is selected for its -60dB depth and 36dB variable attenuation range when the tunable refractive index change is
0.01. We also study different shapes of micro-heaters for low power consumption and high heat transfer efficiency. A
24.6mW and 75.9% heat transfer efficiency are achieved in a 2&mu;m-wide right-angle-shaped micro-heater. In experiment,
A 4.6nm red shift at the cutoff wavelength of the fundamental mode and a 10dB tunable attenuation range are achieved
through tuning the temperature of the W1 PCWG by an 4.7&mu;m-wide aluminum micro-heater with a maximum power
consumption as low as 30.7mW.

The enhanced optical absorption in solar cells using nanoscale structure and novel physical effect has received a lot of
attention in recent years. One of the promising methods is to utilize the noble metal nanoparticles with plasmonic effect
for increasing the light absorption, consequently the conversion efficiency of photovoltaic devices. While the bare metal
nanoparticles may suffer from the energy loss introduced by themselves due to the recombination of electro-hole pairs.
Here, we propose to apply the plasmonic metal-dielectric core-shell nano-particles to improve the optical absorption
efficiency of thin film solar cells. It is expected that the metal core could increase the optical absorption of thin film solar
cells due to the filed enhancement effect of localized surface plasmon (LSP), and meanwhile the dielectric shell could
avoid the metal core to become a new recombination center of the light-induced excitons. Further, varying the refractive
index of the dielectric shell could adjust the enhancement region of LSP in a large range to cover the whole wavelength
range of solar cells. Simulations are carried out by means of the finite element method in a three-dimensional model. The
results show that the absorption enhancement up to 110% could be obtained when the active layer of thin film organic
solar cells is 30nm thick. Then, some initial experiments have been done. The Au-citrate core-shell nanoparticles
synthesized by the sodium citrate reduction method are deposited on the solar cells. And the obvious photocurrent
enhancement has been observed.

Spontaneous four-wave mixing (SFWM) in optical fibers is an important way to generate correlated/entangled photon pairs. When the pulsed pump light passes through the optical fiber, two kinds of SFWM will take place simultaneously. One is scalar scattering processes, in which two annihilated pump photons and generated photon pair are all polarized along the same fiber polarization axis. The other is vector scattering processes, in which two annihilated pump photons are polarized along different fiber polarization axes, either to the two photons of the generated pair. If the fiber has large group birefringence, the intensity of vector scattering processes will be suppressed at the phase matching frequencies of the scalar scattering processes. On the other hand, the walk-off effect of the pump pulse components polarized along the two fiber polarization axes also suppresses the vector scattering processes. Hence, by proper pump polarization and signal/idle frequency selection, photon pairs can be generated only by the two independent scalar scattering processes in optical fibers with birefringence, which provide a simple way to realize polarization entangled photon pair generation. In this paper, related experiments based on the high nonlinearity microstructure fiber (HN-MSF) with group birefringence and polarization maintained dispersion shifted fiber (PM-DSF) are introduced, showing their potential on developing practical quantum light sources.

In this paper, correlated photon pairs at 1.55&mu;m are generated in a silicon wire waveguidewith a length of 1.6 mm. The
ratio between coincidence count rate and accidental coincidence count rate under room temperature is 19, showing the
property of low Raman noise and strong quantum correlation. Moreover, the experiment shows that photon pair
generation isstrongly dependent on pump polarization direction. Using quantum perturbation theory, we analyze the
contribution of scalar and vectorspontaneous four-wave mixing processes to the generated photon pairs. Due tohigh
nonlinear coefficient and high coupling efficiency, the generation rate in quasi-TE mode is much larger than that in
quasi-TM mode.The combination of calculated photon pair generation rates through scalar and vector spontaneous four-wave
mixing processes agrees well with the experimental result.

Near-infrared silicon solar cell response enhanced by gold nanoparticles with core-shell structure has been studied
experimentally. The colloidal core-shell gold nanoparticles are synthesized by the standard sodium citrate
reduction method. The enhanced photocurrent response of silicon solar cell is obtained over almost the entire
silicon response spectrum, and the obvious enhancement is observed when &lambda;0 &gt; 800nm. The highest value 12%
near &lambda;0=1160nm is obtained.

Layer-thickness dependence of Si-nanocrystal (Si-NC) formation induced by furnace annealing in amorphous Si (a-Si)
/SiO<sub>2</sub> multilayers is experimentally demonstrated with a radio-frequency-sputtered sample that has a-Si layers with
different thicknesses. Further, a modified model is developed to explain the Si-NC formation based on the Gibbs free
energy variation and it takes into account the whole formation process including nucleation and following growth. The
theoretical results show that there is a lower limit of Si layer thickness below which the crystal formation cannot occur
for a-Si/SiO<sub>2</sub> multilayers, and the oxide interfaces cannot constrain the lateral growth of Si-NCs, which may lead to their
touches within the Si layers.

A hollow-core Bragg fiber with the fundamental photonic crystal bandgap around 3000 cm<sup>-1</sup> was fabricated and injected
with methane/nitrogen mixed gas with 0.5% methane concentration. A very sharp absorption line of methane gas around
3000 cm<sup>-1</sup> within the transmission band of hollow-core Bragg fiber was observed using the Fourier transform infrared
spectroscopy, which demonstrated that hollow-core Bragg fiber can be used as a mid-infrared waveguide and minimized
gas cell simultaneously, showing great potential in trace gas sensing.

A hybrid coupler composed of a slot plasmonic waveguide and a dielectric waveguide is proposed and its coupling
characteristics are analyzed. The simulation results show that the ultra-small mode of the slot plasmonic waveguide can
be excited efficiently by the dielectric waveguide mode within the coupling length of just several microns, which
provides an interface between the slot plasmonic devices and dielectric devices. Meanwhile, based on this hybrid the
coupler, a highly integrated refractive index sensor could be realized.

The photoluminescence spectra of amorphous silicon rich silicon nitride films with various compositions were
investigated. Two main luminescence peaks were identified for all samples and blueshift of photoluminescence were
observed after annealing treatment. With the help of X-ray photoelectron spectroscopy and Fourier transform infrared
measurement, the chemical composition and bonding environment of samples, which were grown with different reactant
gases flow rates of plasma enhanced chemical vapor deposition, were analyzed. According to all these measurement
results, it is confirmed that the main luminescence centers are radiative recombination defects, such as silicon and nitride
dangling bonds. With proper deposition conditions, all these radiative recombination defects could be activated at the
same time, so that ultra-wide photoluminescence spectra with full width at half maximum of about 250nm ~ 300nm were
obtained in visible region.

We realize the correlated photon pair generation at 1.5&mu;m by spontaneous four-wave mixing in high nonlinear
microstructure fibre with a length of 25m, showing that high nonlinear microstructure fibres have great potential in
bright, high efficiency and compact sources of correlated photon pairs at 1.5&mu;m.

Group velocity dispersion (GVD) and effective mode area (Aeff) of solid core honeycomb cladding photonic crystal fiber (HPCF) with different doping levels are investigated theoretically. Both total internal reflection and photonic bandgap guiding mechanisms are shown to be available in this fiber structure with the changes of doping levels. GVD is shown to be dominated by the large waveguide dispersion corresponding to the fiber structure. Numerical results show that HPCF can achieve small Aeff with low air-filling fraction. One special case is given to demonstrate the potential of HPCF in dispersion compensation.

Spontaneous parametric down-conversion in two-dimensional photonic crystal made of semiconductor material with large quadratic nonlinear susceptibility is proposed to generate polarization entangled photon pairs. On one hand, the large quadratic nonlinear susceptibility of AlGaAs crystal insures the high nonlinear conversion efficiency; on the other hand, the abnormal dispersion property of two-dimensional photonic crystal causes the satisfaction of the phase-matching condition. In particular, the dispersion property sensitively depends on the structure of photonic crystal. Then the walk-off between the down-converted photons with orthogonal polarizations can be minimized through appropriate structure parameter design; hence compensation measures to mitigate labeling effect on polarization entangled photon pairs can be eliminated.

Group velocity dispersion (GVD) and effective mode area (Aeff) of solid core honeycomb cladding photonic crystal fiber (PCF) with different up/down doping levels are investigated theoretically. Both total internal reflection (TIR) and photonic bandgap (PBG) guiding mechanisms are shown to be available in this fiber structure with gradual change of the doping level. It is noted that the previously overlooked TIR guiding design with up-doping could acquire improved nonlinear property compared with PBG mechanism in short normalized wavelength region. On the other hand, the total GVD is shown to be dominated by waveguide dispersion corresponding to the fiber structure. Numerical results show that HPCF can achieve small Aeff with low air-fill fraction, and doping level in HPCF provides an additional way to change GVD excepting structure parameters. Special cases are given to demonstrate the potential of HPCF in combining design of Aeff and GVD, aiming at applications such as Raman amplification and dispersion compensation around 1550nm.

We proposed a novel quasi-three dimensional (3D) photonic crystal (PC), which is composed of 2D PC and 1D distributed Bragg reflector (DBR) structures with a matching layer set between them. The band structures and reflectance of 1D DBR with changed thickness of the matching layer were calculated by 2D plane wave method and transfer matrix method respectively, while the dispersion diagram of the
quasi-3D PCWs both in GaAs/Al<sub>x</sub>O<sub>y</sub> (or Si/SiO<sub>2</sub>) and GaAs/AlAs PCWs were investigated using 2D plane wave method with supercells. Through adjusting the thickness of the matching layer, out-of-plane confinement by the effects of Bragg mirroring and total internal reflection can be achieved simultaneously. Using this quasi-3D PC waveguide structure, a wide transmission band was demonstrated both in GaAs/Al<sub>x</sub>O<sub>y</sub> (or Si/SiO<sub>2</sub>) and GaAs/AlAs material group.

In this paper, the ability of Bragg fiber array to guide optical mode is investigated theoretically. Simulation shows that Bragg fiber array can be looked as a good waveguide to guide inter-fiber modes, which are supported by the external reflection of the 1-D photonic crystal claddings of the Bragg fibers. The mechanism of leakage loss of the inter-fiber is analyzed, showing that the TM01-like mode has the lowest leakage loss and less than 1dB/m leakage loss can be achieve under the wavelength of 10.6&#956;m. As an open waveguide or 2-D microcavity, the Bragg fiber array has wide potential applications including processes of interaction between light and atoms or molecules.

The influences of the Ge doped core to the properties of holey fibers are investigated in this paper. Numerical simulation shows that for holy fibers with conventional triangular transverse structure, proper-doped core can enhance the nonlinear coefficient and shift the near zero flattened dispersion region to long wavelength. By introducing a Ge doped core, a high nonlinearity holey fiber design for 1.55&#956;m is proposed, with a nonlinear coefficient of 22 W<sup>-1</sup>km <sup>-1</sup> and a wavelength region of 165nm in which the dispersion value is within ±1 ps/km/nm.

This paper reported that, using a directly modulated lasers (DMLs) with a ?/8 phase-shifted distributed feedback (DFB) grating, isolator-free 2.5-Gb/s transmission over 138-km non-dispersion-shifted fiber (NDSF) was demonstrated with ?20-dB external optical feedback. The power penalty was 1.7 dB for a bit error rate (BER) of 10-10. Further potential for their low chirp characteristics was also demonstrated by error-free transmission over 200 km without optical feedback. Uncooled transmission performance at 80°C was also investigated. A low power penalty of less than 1.0 dB for a BER of 10-10 was obtained in transmission over 60 km. The good experimental results are due to the characteristics of low chirp and optical feedback resistance that originate from the negative feedback effect of mirror loss (FEML) in ?/8 phase shifted DFB-LDs. Also discussed in this paper is the design of coupling coefficient ?L and of detuning ?? between oscillation wavelength and gain maximum since these parameters strongly affect the DMLs’ transmission characteristics.

This paper describes grating design of distributed feedback laser diodes (DFB-LDs) for use in metropolitan area and access networks and demonstrates improved performance of DFB-LDs with new gratin structures. Dynamic behaviors of DFB-LDs under the external optical feedback were analyzed for conventional uniform grating DFB-LDs and partially corrugated waveguide laser diodes (PC-LDs). A high-resistant characteristic against external optical feedback was achieved by PC-LD with optimized grating structure. The increase of RIN was suppressed to as low as -126 dB/Hz with the external optical feedback of -20 dB. It was also found that feedback effect of mirror loss (FEML) plays an important role in external optical feedback resistance. Furthermore, negative FEML, which suppresses relaxation oscillation, reduces transient chirp under high-bit-rate modulation. FEML is successfully controlled by adjusting phase shift value in phase-shifted DFB-LDs, and very low power penalty transmission was demonstrated by (lambda) /8 phase-shifted DFB-LDs. After 100-km transmissions, a power penalty of less than 1 dB within a wide extinction ratio region form 8.5 to 14.5 dB was demonstrated with 2.5 Gb/s direct modulation. These DFB-LDs with new grating structure is promising for intermediate transmission applications.

A high-yield and high-performance single longitudinal mode laser diode (LD) is essential for implementing a low-cost optical module for high capacity access networks. We have realized novel partially corrugated waveguide (PC) LDs and shown that they are cost-effective. Because of a unique resonance feature in a mirror loss profile, the PC-LD has higher yield in single longitudinal mode operation than that of a conventional distributed feedback (DFB) LD. The yield of the PC-LD with single-mode stability ((Delta) (alpha) L &gt; 0.3) was theoretically predicted to be as high as &gt; 65%, which is 1.5 to 2 times higher than that of a conventional DFB-LD. Side-mode suppression ratio was experimentally as high as 40 to 50 dB. Uncooled high-efficiency characteristics have been realized for a cavity with asymmetrical reflectivity facets. The threshold current and slope efficiency were 16 mA and 0.26 W/A at 85 degree(s)C. By introducing a spot-size converted waveguide with chirped corrugation, butt-coupling efficiency was improved by 3 dB higher than that of the conventional straight waveguide. Furthermore, excellent optical feedback resistant 622 Mb/s operation has been demonstrated over a wide temperature range of -40 to 85 degree(s)C. The power penalty was as low as 1 dB under the optical feedback level of -8.5 dB. Isolator-free 2.5 Gb/s-70 km transmission was also demonstrated. The PC-LDs with this performance are very promising for realizing cost-effective optical modules for use in high capacity optical access networks.

This paper clarifies superior external optical feedback resistant characteristics in partially-corrugated-waveguide laser diodes (PC-LDs), compared to conventional distributed feedback laser diodes (DFB-LDs). Based on a novel large single dynamic analysis by using the van der Pol equations in single-mode laser diodes (LDs), it is found that the external optical feedback resistance in single-mode LDs is dominated by the transient fluctuation of mirror loss (total net threshold gain), and depends on the grating phases at the cleaved facets. Theoretical results predict that in the PC-LDs, mirror loss is insensitive to the grating facet phases due to a unique waveguide, which consists of a corrugated waveguide near the antireflection-coated front facet and an uncorrugated waveguide near the high- reflection-coated rear facet. Therefore the variation of phase conditions for oscillation caused by the external optical feedback gives rise to a relative low transient fluctuation of the mirror loss that suppresses the positive feedback effect of mirror loss, as well as the optical output fluctuations. Furthermore, optimum-grating length, i.e. 150 micrometers for 250 micrometers cavity length, was derived by the calculations. The relative intensity noise (RIN) caused by external optical feedback was measured for PC-LDs with different grating length over a wide feedback level range from -40 dB to -20 dB. Experimental results show that, for the cavity length of 250 micrometers , the PC-LDs with a grating length of 150 micrometers have the most excellent external optical feedback resistant characteristics. The increase of RIN was suppressed to as low as -126 dB/Hz with the external optical feedback of -20 dB. These results agreed well with the theoretical analysis.

Recent CATV network systems require high power (P<SUB>o</SUB> &gt;= 20 mW), wide band (1 GHz) and low distortion light sources for use in high capacity network schemes. Furthermore, cost effective light sources are also needed for use in narrowing services. We have developed high performance, 1.3-micrometers partially corrugated waveguide laser diodes (PC-LDs) suitable for use in such CATV networks. The production yield of these PC-LDs with respect to low distortion specifications has been improved about three times over that of conventional distributed feedback (DFB) LDs, and this can be attributed to their characteristic of not being sensitive to grating phases as well as their flat electric field profile along the cavities. Excellent low distortion characteristics (a composite second-order distortion &lt;EQ -60 dBc and a composite triple beat &lt;EQ -70 dBc) for an 80-channel CATV specification were also realized for the PC-LDs over the wide power range of 10 approximately 30 mW by reducing junction capacitance of the current blocking layer. Intermodulation distortion in LDs caused by several nonlinear mechanisms was also investigated using a transfer- matrix method and an electric equivalent circuit model of LDs, taking electric field distribution along the cavity and leakage current that flows into the current blocking layer into account. Resonance oscillation and electric field nonuniformity related distortion are predominant in the lower light-output power region, while leakage current related distortion is dominant in the high-power region. Moreover, external optical feedback resistant characteristics of the PC-LDs were theoretically predicted and experimentally demonstrated. Optical feedback resistance of the PC-LDs was about ten times higher than that of conventional DFB-LDs due to their unique electric field profile along the cavity.

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This course description is available in Chinese at <a href="http://spie.org/Conferences/Programs/03/apoc/shortCourses/APOC_courseListings_Chinese.pdf">http://spie.org/Conferences/Programs/03/apoc/shortCourses/APOC_courseListings_Chinese.pdf</a href>.

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Advanced PhotonicsJournal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews